1. Field of the Invention
The present inventions relate generally to wireless data movement and, more particularly, to how wireless devices maintain consistent network connections when more than one network is present.
2. Background
Wireless networks have evolved from a simple point-to-point link to encompassing different coverage areas at varying data transfer rates. For example, a short ranged network (made up of connectivity devices such as Bluetooth capable devices) provides data rates in excess of 3 Mb/s covering a small room; a medium range network (such as Wi-Fi or 802.11) that provides data rates of 25 Mbps covering a several rooms; a large range network (such as The Global System for Mobile TeleCommunications (GSM)) with cells that provide several hundred kbits/s data rate covering a city; and the largest connectivity devices, satellite networks, provide data coverage for several countries. The multi-mode mobile terminal has capabilities to connect to different networks based on the policies of the user and the network, such as the particular sources that have been purchased or provided. Due to the overlapping of these networks a user can roam through multiple networks during a single session. In all roaming scenarios, the handover mechanism between these hybrid networks is a vital topic.
General Packet Radio Service (GPRS) is a data communication technology that is capable of transferring packet data and signaling in a cost-efficient manner over GSM radio networks while optimizing the use of radio and network resources. The voice traffic and the data packet share the same physical channel, but new logical GPRS radio channels are defined. Data transfer rates up to 171.2 Kbps are possible over GPRS thus enabling mobile data services, like Internet applications, over mobile devices. The data traffic is segregated and sent to a Serving GPRS Support Node (SGSN) node from the BSC. The SGSN node connects to a Gateway GPRS Support Node (GGSN) for communication with external packet data networks. The next generation of this technology is UMTS that provides higher data transfer rates. Typically GPRS and UMTS networks operate over licensed frequencies and are owned by mobile operators. Several entities have created a partnership project called 3GPP that is responsible for defining services, architecture and protocols. These specifications cover wireless access network, core network nodes and interconnection protocols etc.
The Wireless Local Area Network (WLAN) is a wireless extension to Ethernet LAN technologies. The IEEE 802.11 committee has defined several of these standards and named them 802.11b, 802.11g and 802.11a. In WLAN, each service access point (AP) covers a cell. In IEEE 802.11, each single cell is defined as a basic service set (BSS). Several BSSs can form an extended service set (ESS). IEEE 802.11 only defines the communication between the client (referred to also as the mobile terminal (MT) or mobile node (MN)) and access point (AP) (the physical layer and data link layer). The client connects to the AP that has higher signal quality and communicates wirelessly to the AP. The data communication is similar to the wired Ethernet communication except for the physical layer and medium access.
802.11x WLAN technologies, popularly known as the Wi-Fi, have become predominant in the limited mobility wireless data networks due to reasonably higher data transfer rates and affordability of the technology. In fact, 3GPP has come up with a specification (TS 23.234) on how to interwork WLAN with GPRS/UMTS networks. Both these wireless technologies are complimentary in several aspects. Therefore, many operators provide both services, with GPRS for global roaming and Wi-Fi for limited mobility areas popularly known as hotspots. There are several devices that support these dual technologies paving way for pervasive computing. The hotspots are WLAN islands scattered at key geographic locations. The mobile user would be roaming between GPRS coverage area and Wi-Fi coverage area very frequently thus requiring a fast and efficient handover procedure.
To achieve seamless mobility, the client should do fast handover from GPRS network to WLAN or vice versa without interruption. Several methodologies have been proposed for this roaming scenario. Two different methodologies that address this problem are described below.
Background: Mobile IP
Mobile IP (MIP) provides mobility at the network layer thus enabling roaming between different networks. The MIP is specified in Request for Comments (RFC) 3344 (for IPv4) and 3775 (for IPv6) by the Internet Engineering Task Force (IETF) community. MIP defines two nodes, Home Agent (HA) and Foreign Agent (FA). The HA is the coordinating node on the home network of a user. The mobile node communicates to HA node directly, using normal IP routing, when connected to the home network. A Foreign Agent is a node in a MIP network that enables roamed IP users to register on the foreign network. The FA will communicate with the HA (Home Agent) to enable IP data to be transferred between the home IP network and the roamed IP user on the foreign network. Whenever the node is connected on a foreign network, it acquires a care-of-address (COA) and registers with the HA providing the COA. The data packets sent by a correspondent node (CN) destined to the mobile node are captured by HA in the home network and are tunneled to the COA. The packets are decapsulated either at FA or client. When the client roams to another network, it acquires new COA and registers with HA about its new location. Now all the data packets destined to this mobile node are tunneled to the new COA.
One common solution for GPRS and WLAN mobility using MIP is to provide home agent (HA) functionality at the Gateway GPRS Support Node (GGSN). The FA functionality can be at Serving GPRS Support Node (SGSN) for the GPRS network and at the Wireless Gateway (WG) for the Wide Area Local Network (WLAN). Otherwise a co-located Care of Address (COA) can be used if the client supports MIP.
FIG. 1 illustrates this type of communication network. A GGSN 102 is connected to both a SGSN 104 and a WLAN Gateway 106. There is generally a constant connection between the GGSN, SGSN, and WLAN Gateway. A HA 112 is located north of GGSN, which, in this embodiment, means that the HA is connected directly to the GGSN which is connected to the client networks 104 and 106. Clients 108, 110 may connect to the GGSN through either the SGSN or through the WLAN Gateway. The GGSN provides connectivity to an IP network such as the Internet. When the client is connected through GPRS network, it acquires the remote IP address from the GGSN. This GGSN-assigned IP address works as the COA and the client registers this COA to the HA. When the client moves into WLAN area and connected to the WLAN, it acquires the IP address from either NAS or WLAN gateway. This IP address is different from the GGSN-assigned IP address and it serves as a new COA. The client registers this IP address to the HA. Since the client's home address remains the same and only the COA is changed, the mobility can be supported with the service continuity.
Though MIP provides mobility between these two networks the handover is not seamless because of the time delay from the point the client moves to a different network and the registration with the HA is completed. During this phase, HA sends all packets for client towards the old COA and these packets could be lost. This is a problem when roaming from WLAN to GPRS network since the WLAN connection is gone and any packets sent over this network will not reach the client. The other drawback of this solution is the triangle routing of the data packets (the packets from client to the correspondent node (CN) are directly routed while the packets from CN are sent to HA first and then tunneled to client) that is inherent in the MIP. Route optimization methods have been proposed to overcome this issue. Finally, there are 3GPP services that are valuable to operators and useful to end-users. Such services are accessible at the GGSN and Mobile IP layer makes this work complicated. In other words, since the anchor point is HA and all the packets should be decapsulated at HA, the service differentiation using APN (Access point name) at GGSN is not simple. GGSN also can perform some services, e.g. content-based billing, and this gets more complicated because of MIP tunneling. The MIP packet overhead in all the packets (both GPRS and WLAN) and message overhead for registration is one drawback, too.
Background: Inter-SGSN Like Handover Approach
The WLAN coverage cell is small compared to the cell of the GSM area. One method of integrating these two networks is by treating the WLAN as a smaller network within the GSM network. Several Access Points (AP) connecting to a WG represent a small coverage area. In “Method and System for Transparently and Securely Interconnecting a WLAN Radio Access Network into a GPRS/GSM Core Network.” it has been demonstrated how the WG could function in a manner similar to the SGSN and thereby providing an interconnection into GPRS core network. The roaming scenario is just like an Inter-SGSN Routing Update process described in the GPRS specification. When the client roams in to WLAN area, the client sends the Routing Area Update request to the WG. To retrieve all the MM and PDP contexts for the client, WG requests these contexts from previous serving SGSN. After the contexts are transferred to WG, SGSN starts forwarding all the packets to WG, if it receives any packets from GGSN. The WG now, based on the information of the existing GPRS PDP context, sends an Update PDP Context to the GGSN that will transfer the existing GPRS session to this network.
The GGSN sends a packet data protocol/mobility management context standby command to the old SGSN. The message is to ask the SGSN to hold the PDP/MM context till the client comes back to the UMTS or detaches. The packets are sent over the WLAN through WG to the GGSN and the IP address of the session still remains the same. When the client roams back to the GPRS network, a Routing Area (RA) update procedure is triggered that activates the old GPRS session. The handover delay in this process is lower than that of the Mobile IP method described earlier. Due to the tight integrated nature of this solution, the LAN based architecture on the WLAN needs several changes to accommodate this solution. Especially WG should support most of standard GPRS SGSN functionalities. Also, the client should be intelligent enough to obtain the GPRS session parameters and sends it to the WG. Since it is not an open architecture solution, this method is not preferred.
Maintaining Consistent Network Connections While Moving Through Wireless Networks
Handover between different wireless access networks (e.g., a GPRS access network and a WLAN access network) is facilitated by a proxy server (also referred to herein as a proxy server or proxy, which can optionally be combined with a global wireless gateway node) preferably adapted to communicate with other nodes of a network, such as nodes of a GPRS network and/or a WLAN. (Note that hereinafter, the term SGSN may be referred to a server GSN, and a GGSN can be referred to as a gateway GSN.)
In one example class of embodiments, when a multifunction (e.g., dual mode) client is operating as a GPRS client (i.e., it is using a GPRS access network), the DNS server is configured to resolve the selected APN to the proxy server's high-level address, so that all control traffic is sent to the proxy server, preferably prior to being sent to another node, such as a GGSN.
In embodiments wherein the user equipment or mobile node accesses the network via a GPRS access network, the user traffic may flow from an SGSN through the proxy server to a GGSN, or the user traffic can flow directly to the GGSN, without first passing through the proxy server, therefore reducing the number of hops for user data. When a handover to another type of access network occurs (e.g., to a WLAN access network) preferred embodiments implement one of at least two options: if only control traffic was anchored at the proxy server, then the proxy server can update the GGSN to switch the user traffic from SGSN to the proxy server. GGSN would typically reflect this in its accounting. Alternatively, if both control and user traffic were anchored at the proxy server, the proxy server can do a simple update to the GGSN for accounting purposes, since data and control flow are already established with the GGSN through proxy server.
In either case, on handover (e.g., from a GPRS to a WLAN access network) the client preferably establishes a tunnel to the proxy server as its wireless gateway. When the handover happens, the proxy server already has all the control information of the GPRS session, because the control traffic passes through the proxy server, preferably no matter what access network is used.
In embodiments wherein the user equipment uses a WLAN access network, it is preferred that both control and user traffic are routed through the proxy server, and the proxy server acts as a wireless gateway server.
Traffic on the “access side” of the proxy server can thus take different paths, depending on the access network used by the user equipment. Traffic on the other side of the proxy server (e.g., toward a GGSN or other node) is preferably unchanged when the user equipment changes access networks. This efficient means of handover between access networks is facilitated by preferred embodiments' use of the proxy server to receive control traffic for the session.
In preferred embodiments, the present innovations are implemented using an address mapping mechanism that is internal to the proxy server and another node, such as a DNS server (as part of a GPRS network). The DNS server, which normally points traffic to a GGSN, instead points to the proxy server. The proxy server includes an address mapping mechanism that points in turn to the GGSN. As stated above, either control traffic or both control and user traffic are proxied in this way, depending on the specific implementation.
Thus the present innovations provide, in preferred embodiments, efficient handover between two types of access networks, retaining at least part of the connection to a target or destination network.
The proxy server thus allows the change in route to be invisible to the GGSN. Consistent connections may therefore be maintained with the same application-layer address and optimized even when data is routed through varying networks.
The disclosed inventions, in various embodiments, provide at least the following advantages:                Each application's data connections are not perturbed by movement, since changes in the client's local IP address can be concealed from at least some processes and the same application layer IP address can be used across different access networks.        Complexities due to access changes are HIDDEN from applications.        The GGSN can still operate normally, and does not have to know what the proxy server is doing, therefore supporting the handover with no or minimum changes to the existing GGSN node itself        The client can still operate normally, and does not have to know about the proxy server, therefore supporting the handover with no or minimum changes to the existing client itself.        If the DNS server for a selected APN does not point to the proxy server, then conventional operation will occur, and the rest of the network is not impacted.        The handover mechanisms enabled by the proxy server and found in some embodiments of the inventions preserve the address of the client with minimal messaging overhead.        Consistent connections may therefore be maintained and optimized even when data is routed through varying networks.        A centralized proxy server can optionally maintain records for billing and usage purposes for all varying services (especially in the case where the proxy server is handling both data and control).        A centralized proxy server can optimize traffic flow over a wide range of networks.        A centralized proxy server can maintain a unique identifier while a client travels through different ISP's        